1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunctional peripheral (MFP) including these functions thereof, to be more specific, relates to an image forming apparatus including an image carrier that carries a toner image and a transfer member that abuts against the image carrier in a pressurized manner to form a transfer nip and transfers the toner image onto a recording medium.
2. Description of the Related Art
In electrophotography image forming apparatuses using intermediate transfer members such as intermediate transfer belts and secondary transfer units including secondary transfer rollers, there has been a problem that positions of the intermediate transfer member and the secondary transfer unit are difficult to be defined with a configuration in which the secondary transfer unit is fixed onto a drawer that can be drawn from an image forming apparatus main body. Therefore, positional accuracy of the secondary transfer unit and the intermediate transfer member has been enhanced by fixing the secondary transfer unit onto the drawer with high accuracy.
For example, in Japanese Patent Application Laid-open No. 2004-144878, the following configuration has been disclosed. That is, a secondary transfer device is held on a sub housing in an unfixed state through a biasing unit, and if the sub housing is accommodated in a main housing for holding a secondary transfer belt, the secondary transfer device is positioned with respect to the secondary transfer belt in the main scanning direction with a biasing force of the biasing unit. In Japanese Patent Application Laid-open No. 2004-144878, the alignment accuracy of the members on a so-called drawer is guaranteed so as to try to ensure stable conveyance property and image quality. Furthermore, in Japanese Patent Application Laid-open No. 2002-296927, the following configuration has been disclosed. That is, an outer diameter of a swing support shaft is manufactured to be slightly smaller than an inner diameter of a fitting hole of a support frame into which the swing support shaft is fitted so as to make a fitting portion have backlash for keeping a pressing force to be substantially uniform when a transfer device is positioned and is made to abut against an image carrier, and positional deviation and parallelism are corrected with the backlash.
However, with the configuration in which the secondary transfer unit is positioned on the drawer strictly, accuracy of the secondary transfer unit and the intermediate transfer belt is not obtained sufficiently due to deflection or tolerance of the drawer, resulting in adverse influence on image formation with high image quality.
There is a need to fix a transfer member and an image carrier with high accuracy and make it possible to prevent deterioration in image quality due to pressure deviation or the like.